heat sink transmission oil cooler

Every trans cooler I've seen is an auxiliary cooler, as in you plumb it in line with your radiator cooler. The trans fluid needs to be a certain temp to work efficiently too cold is bad, tooh to is bad. I've seen OE setups with auxiliary coolers with a thermostat to bypass the auxiliary cooler until a certain temp is reached. I'm talking pure street cars here so race setup may vary.